Transflective switchable double-cell LCD device

ABSTRACT

To be realized the well-lighted display by using the whole pixels in the reflective mode and the transmissive mode. In a reflective mode, an optical element  13  is used as liquid crystal display element. That is, the optical element  13  operates as liquid crystal display element by applying the voltage. In this case, the optical element  13  reflects the external light since the optical element  13  is a scattering state with regard to non-applying pixel (arrow B). In a transmissive mode, a liquid crystal panel  12  is used as liquid crystal display element. That is, the liquid crystal panel  12  operates as liquid crystal display element by applying the voltage. In this case, the optical element  13  passes light from a backlight  11  since the optical element  13  is a transmissive state (arrow A). And the optical element  13  plays a color filter part and does not operates as display element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the transflective liquid crystaldisplay device, particularly to the transflective liquid crystal displaydevice usable the whole pixels in the reflective mode and thetransmissive mode.

2. Description of Related Art

So-called transflective liquid crystal display devices have been putinto full-scale practical use in which external light incident from afront side is reflected to lead to the front side, while incident lightfrom a rear side due to the backlight system is transmitted to lead tothe same front side. The liquid crystal display devices of this typeprovide effective image display by the external light (ambient light)principally (reflective mode) under well-lighted environments, and bythe emitted light in the backlight system principally (transmissivemode) under low light environments.

Such a type of liquid crystal display device is disclosed in a documentof the related art of M. Kubo, et al. “Development of Advanced TFT withGood Legibility under Any Intensity of Ambient Light”, IDW“99,Proceedings of The Sixth International Display Workshops, AMD3–4, pages183–186, Dec. 1, 1999, sponsored by ITE and SID”.

In this device, each pixel has a reflective region and a transmissiveregion. The reflective region is provided with, for example, an aluminumreflecting member. The transmissive region is formed by removing part ofthe reflecting member. For example, the transmissive region is arrangedat the center in a rectangular pixel region and has a rectangular shapesubstantially geometrically similar to the pixel region. The reflectiveregion is a portion of the pixel region except the rectangulartransmissive region and has a shape of surrounding the transmissiveregion.

However, in the above-mentioned transflective liquid crystal displaydevices, since a single pixel has a transmissive region and a reflectiveregion, there are disadvantages that the transmittance ratio is lowerthan that in the transmissive type liquid crystal display device, whilethe reflectivity is lower than that in the reflective type liquidcrystal display device. In other words, in terms of luminosity,transflective liquid crystal display devices are unfavorable as comparedwith transmissive type liquid crystal display devices and reflectivetype liquid crystal display devices.

In view of the present invention, it is an object of the presentinvention to provide a transflective liquid crystal display deviceenabling well-lighted display using the whole pixels in both areflective mode and transmissive mode.

SUMMARY OF THE INVENTION

The subject matter of the present invention is to realize thewell-lighted display with a same level as that in the transmissive typeLCD or the reflective type LCD by disposing an optical element, which iscapable of switching between transmission of light from a light sourceand reflection of external light by applying the voltage, between thelight source and liquid crystal panel or over the liquid crystal panel,and thereby using the whole pixels in the reflective mode and thetransmissive mode of the transflective LCD.

A transflective liquid crystal display device of the present inventionis a transflective liquid crystal display device which has a reflectivemode using external light and a transmissive mode using a light source,and has a light source used in the transmissive mode, a liquid crystalpanel, arranged over the light source, for operating as a displayelement in the transmissive mode, and an optical element, arranged overthe liquid crystal panel, for operating as a display element in thereflective mode.

According to this arrangement, since the optical element, which switchesbetween transmission of light from the light source and reflection ofexternal light by applying the voltage, is arranged over the liquidcrystal panel, well-lighted display can be realized in either thetransmissive mode or the reflective mode using the whole pixels. In thisarrangement, using a polymer type liquid crystal display element as anoptical element eliminates the need of a polarizer in the opticalelement, and therefore, it is possible to perform well-lighted displayextremely in the reflective mode.

It is preferable in the transflective liquid crystal display device ofthe present invention that the optical element passes light from thelight source in the transmissive mode and reflects the external light inthe reflective mode.

The transflective liquid crystal display device of the present inventionis preferably provided with switching control means for switchingcontrolling the power supply such that the liquid crystal panel operatesas a display element in the transmissive mode and the optical elementoperates as a display element in the reflective mode.

It is preferable in the transflective liquid crystal display device ofthe present invention that the optical element has an arrangement ofpixel and has a color filter.

A transflective liquid crystal display device of the present inventionis a transflective liquid crystal display device which has a reflectivemode using external light and a transmissive mode using a light source,and has a light source used in the transmissive mode, an opticalelement, arranged over the light source, for passing light from thelight source in the transmissive mode and for reflecting the externallight in the reflective mode, and a liquid crystal panel, arranged overthe optical element, for operating as a display element.

According to this arrangement, since the optical element, which switchesbetween transmission of light from the light source and reflection ofexternal light by applying the voltage, is arranged between the lightsource and the liquid crystal panel, well-lighted display can berealized in either the transmissive mode or the reflective mode usingthe whole pixels. In other words, it is possible to deliver optimumperformance in both the transmissive mode and the reflective mode.

The transflective liquid crystal display device of the present inventionis preferably provided with switching control means for switchingcontrolling the power supply such that light from the light source ispassed through the optical element in the transmissive mode and theexternal light is reflected by the optical element in the reflectivemode.

In the transflective liquid crystal display device of the presentinvention, it is preferable that the optical element has a polymerdispersed type liquid crystal display element or a polymer network typeliquid crystal display element.

Further scope of the applicability of the present invention will becameapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a view showing an arrangement of the transflective liquidcrystal display device according to Embodiment 1 of the presentinvention;

FIG. 2 is a sectional view showing an arrangement of the liquid crystalpanel of the transflective liquid crystal display device according toEmbodiment 1 of the present invention;

FIG. 3 is a sectional view showing an arrangement of the optical elementof the transflective liquid crystal display device according toEmbodiment 1 of the present invention;

FIG. 4 is a block diagram showing an arrangement of the transflectiveliquid crystal display device according to Embodiment 1 of the presentinvention;

FIG. 5 is a view showing a switching table in the transflective liquidcrystal display device according to Embodiment 1 of the presentinvention;

FIG. 6 is a view showing an arrangement of the transflective liquidcrystal display device according to Embodiment 2 of the presentinvention;

FIG. 7 is a sectional view showing an arrangement of the liquid crystalpanel of the transflective liquid crystal display device according toEmbodiment 2 of the present invention;

FIG. 8 is a sectional view showing an arrangement of the optical elementof the transflective liquid crystal display device according toEmbodiment 2 of the present invention; and

FIG. 9 is a block diagram showing an arrangement of the transflectiveliquid crystal display device according to Embodiment 2 of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Embodiments of the present invention will be described specificallybelow with reference to accompanying drawings.

This embodiment describes an arrangement where an optical element, whichis capable of switching between transmission of light from the lightsource and reflection of external light by applying the voltage, isarranged over the liquid crystal panel. FIG. 1 is a view showing anarrangement of the transflective liquid crystal display device accordingto Embodiment 1 of the present invention.

The transflective liquid crystal display device as shown in FIG. 1principally has a backlight 11 that is the light source used in thetransmissive mode, a liquid crystal panel 12, arranged over thebacklight 11, for operating as a display element in the transmissivemode, and an optical element 13, arranged over the liquid crystal panel12, for operating as a display element in the reflective mode.

As the backlight 11, there may be backlights used in general liquidcrystal display devices.

Liquid crystal panels used in monochrome transmissive type LCD, forexample, TN (Twisted Nematic) liquid crystal panel and STN (SuperTwisted Nematic) liquid crystal panel, may be used as the liquid crystalpanel 12. Further, an active matrix liquid crystal panel may be used,and thus various types of liquid crystal panels may be used irrespectiveof liquid crystal type, driving method and alignment mode (for example,VA (Vertical Alignment) and IPS (In Plane switching)). For example, aliquid crystal panel with an arrangement as shown in FIG. 2 may be usedas the liquid crystal panel 12.

FIG. 2 is a sectional view showing an arrangement of the liquid crystalpanel of the transflective liquid crystal display device according toEmbodiment 1 of the present invention. A transparent electrode 23 isformed on one main surface of a glass substrate 21 on one side. Asmaterials for the transparent electrode 23, for example, there may beITO (Indium Tin Oxide), zinc oxide series materials, titanium oxideseries materials, indium oxide-zinc oxide series materials, Ga dopedzinc oxide series materials, and p-type oxide materials. An alignmentfilm 24 is formed on the transparent electrode 23. As materials for thealignment film 24, there may be resin materials such as polyimide.

As in the glass substrate 21, a transparent electrode 25 is formed onone main surface of a glass substrate 22 on the other side, and analignment film 26 is formed on the transparent electrode 25. Asrespective materials for the transparent electrode 25 and alignment film26, the same materials as in the glass substrate 21 may be used.

In addition, transparent electrodes 23 and 25 respectively on glasssubstrates 21 and 22 compose matrixes of scanning electrode and signalelectrode to enable the display. Further, as methods of forming thetransparent electrodes 23 and 25, there may be methods used inmanufacturing general liquid crystal display devices such as sputtering,for example. As methods of forming alignment films 24 and 26, there maybe methods used in manufacturing general liquid crystal display devicessuch as methods including processes of coating, drying, and rubbing, forexample.

A liquid crystal layer 27 is formed between the glass substrates 21 and22. The liquid crystal layer 27 is formed by arranging the glasssubstrates 21 and 22 on which films are formed so that the alignmentfilms 24 and 26 are opposed to each other, and filling a liquid crystalmaterial (herein, TN liquid crystal) between the glass substrates 21 and22. A polarizer 28 is arranged on the other main surface of the glasssubstrate 21, and a polarizer 29 is arranged on the other main surfaceof the glass substrate 22. In addition, while the example is hereindescribed where the polarizer comprised of a single sheet is used, inthe present invention it may be possible to use a polarizer comprised ofa plurality of sheets including a retardation film and optical film forviewing angle compensation.

A polymer network type liquid crystal display element and polymerdispersed type liquid crystal display element may be used as the opticalelement 13. For example, it may be possible to use a polymer networktype liquid crystal display element with an arrangement as shown in FIG.3.

FIG. 3 is a sectional view showing an arrangement of the optical elementof the transflective liquid crystal display device according toEmbodiment 1 of the present invention. A transparent electrode 33 isformed on one main surface of a glass substrate 31 on one side. A colorfilter 36 is formed on one main surface of a glass substrate 32 on theother side. A transparent electrode 34 is formed on the color filter 36.Methods used in manufacturing general liquid crystal display devices maybe used as methods of forming the color filter 36 and transparentelectrodes 33 and 34. The same materials as those used in the liquidcrystal panel 12 may be used as materials for the transparent electrodes33 and 34, and as methods of forming the electrodes, there may bemethods used in manufacturing general liquid crystal display devices. Inaddition, the transparent electrodes 33 and 34 respectively on glasssubstrates 31 and 32 compose matrixes of scanning electrode and signalelectrode to enable the display.

A polymer liquid crystal layer 35 is formed between the glass substrates31 and 32. The polymer liquid crystal layer 35 is sandwiched between theglass substrates 31 and 32 arranged so that the transparent electrodes33 and 34 are opposed to each other. As the polymer liquid crystal layer35, it may be possible to use a polymer network type liquid crystalwhere networks containing liquid crystal molecules extend in a polymermatrix and a polymer dispersed type liquid crystal where liquid capsulescontaining liquid crystal molecules are dispersed in a polymer matrix.In addition, in terms of low driving voltage, the polymer network typeliquid crystal is more advantageous.

The liquid crystal panel 12 and optical element 13 are arranged in theorder of the backlight 11, liquid crystal panel 12 and optical element13 as shown in FIG. 1. In this arrangement, the liquid crystal panel 12is used as a display element in the transmissive mode, and the opticalelement 13 is used as a display element in the transflective mode.

FIG. 4 is a block diagram showing an arrangement of the transflectiveliquid crystal display device according to Embodiment 1 of the presentinvention. The arrangement has a control section 41 that controls theentire device, a switching control section 42 that controls switching ofapplication of voltage to the backlight 11, liquid crystal panel 12, andoptical element 13, and power supply 43 that supplies the power for theapplication of voltage. Further, the arrangement has switches SW1 to SW3to perform switching control. The switching control section 42 has aswitching table as shown in FIG. 5, and based on the switching table,performs the switching control.

The operation in the transflective liquid crystal display device withthe above-mentioned arrangement according to this embodiment will bedescribed below.

Based on an input from a user or external circumstances (such asluminance and quantity of light), the control section 41 automaticallysets a display mode (reflective mode or transmissive mode), and outputsthe mode information to the switching control section 42. The switchingcontrol section 42 controls switching of power supply to SW1 to SW3 soas to use the optical element 13 as a display element using the externallight in the reflective mode, while using the liquid crystal panel 12 asa display element using the light from the backlight 11 in thetransmissive mode.

A case of the reflective mode will be described first. In the reflectivemode, specifically, as shown in FIG. 5, since the optical element 13 isused as a display element, SW1 is ON. In the reflective mode, since theoptical element 13 is used as a display element, the voltage is notapplied to the liquid crystal panel 12. Therefore, SW2 is OFF. Further,in the reflective mode, since the external light is used, the power isnot supplied to the backlight 11 either. Thus, SW3 is OFF either.

In such a state, the optical element 13 is driven as a general liquidcrystal display element. In other words, the power supply 43 suppliesthe power to apply the voltage to the optical element 13 for thedisplay. In this case, the optical element 13 reflects the externallight since the optical element 13 is a scattering state with regard tonon-applying pixel (arrow B in FIG. 1).

A case of the transmissive mode will be described next. In thetransmissive mode, specifically, as shown in FIG. 5, since the voltageis applied to the optical element 13 to be a transmissive state to passthe external light, SW1 is ON. In the transmissive mode, since theliquid crystal panel 12 is used as a display element, the voltage isapplied to the liquid crystal panel 12. Therefore, SW2 is ON also.Further, in the transmissive mode, since the external light is not used,the power is supplied to the backlight 11. Thus, SW3 is ON also.

In such a state, the liquid crystal panel 12 is driven as a generalliquid crystal display element. In other words, the power supply 43supplies the power to apply the voltage to the liquid crystal panel 12for the display. In this case, the light from the backlight 11 is outputto the outside since the optical element 13 is a transmissive state(arrow A in FIG. 1). Further, the optical element 13 plays a role as acolor filter and does not operate as a display element.

Thus, in the transflective liquid crystal display device according toEmbodiment 1, since the optical element, which switches betweentransmission of light from the backlight and reflection of externallight by applying the voltage, is arranged over the liquid crystalpanel, well-lighted display can be realized in either the transmissivemode or the reflective mode using the whole pixels. In other words, itis possible to deliver optimum performance in both the transmissive modeand the reflective mode.

Further, in this arrangement, since the optical element does not requirea polarizer, it is possible to perform well-lighted display extremely inthe reflective mode. Furthermore, in this embodiment, it is not requiredto provide a transmissive region (hole) in a pixel, and therefore, it isalso possible to simplify manufacturing processes.

While this embodiment describes the arrangement where application ofvoltage to the optical element 13 is switched, by using an arrangementwhere the scattering degree is associated with grayscale in a polymertype liquid crystal of the optical element 13, it is possible to realizegrayscale display by performing both the reflective display andtransmissive display. In this case, the power is supplied to all theoptical element, liquid crystal panel and backlight, and the voltageapplied to the optical element is controlled. It is thereby possible tocontrol priorities of modes to use in user preferential.

This embodiment describes an arrangement where an optical element, whichis capable of switching between transmission of light from the lightsource and reflection of external light by applying the voltage, isarranged between the light source and the liquid crystal panel. FIG. 6is a view showing an arrangement of the transflective liquid crystaldisplay device according to Embodiment 2 of the present invention.

The transflective liquid crystal display device as shown in FIG. 6principally has a backlight 61 that is the light source used in thetransmissive mode, an optical element 62, arranged over the backlight61, for switching transmission of the light from the backlight 61 andreflection of the external light by applying the voltage, and a liquidcrystal panel 63, arranged over the optical element 62, for operating asa display element in the transmissive mode.

As the backlight 61, there may be backlights used in general liquidcrystal display devices.

Liquid crystal panels used in monochrome transmissive type LCD, such as,for example, TN (Twisted Nematic) liquid crystal panel and STN (SuperTwisted Nematic) liquid crystal panel, may be used as the liquid crystalpanel 63. Further, an active matrix liquid crystal panel may be used,and thus various types of liquid crystal panels may be used irrespectiveof liquid crystal type, driving method and alignment mode (for example,VA (Vertical Alignment) and IPS (In Plane switching)). For example, aliquid crystal panel with an arrangement as shown in FIG. 7 may be usedas the liquid crystal panel 63.

FIG. 7 is a sectional view showing an arrangement of the liquid crystalpanel of the transflective liquid crystal display device according toEmbodiment 2 of the present invention. In addition, in FIG. 7, the sameportions as in FIG. 2 are assigned the same reference numerals as inFIG. 2 and specific descriptions thereof are omitted.

The transparent electrode 23 and alignment film 24 are successivelyformed on one main surface of one side of the glass substrate 21. Acolor filter 71 is formed on one main surface of the other side of theglass substrate 22, and as in the glass substrate 21, the transparentelectrode 25 and alignment film 26 are formed on the filter 71successively. The same materials as in Embodiment 1 may be used asmaterials for each of the transparent electrode 25, alignment film 26and color filter 71.

In addition, the transparent electrodes 23 and 25 respectively on theglass substrates 21 and 22 compose matrixes of scanning electrode andsignal electrode to enable the display. Further, the same methods as inEmbodiment 1 may be used as methods of forming the transparentelectrodes 23 and 25, methods of forming the alignment films 24 and 26and method of forming the color filter 71.

The liquid crystal layer 27 is formed between the glass substrates 21and 22. The liquid crystal layer 27 is formed by arranging the glasssubstrates 21 and 22 on which films are formed so that alignment films24 and 26 are opposed to each other, and filling a liquid crystalmaterial (herein, TN liquid crystal) between the glass substrates 21 and22. The polarizer 28 is arranged on the other main surface of the glasssubstrate 21, and the polarizer 29 is arranged on the other main surfaceof the glass substrate 22. In addition, while the example is hereindescribed where the polarizer comprised of a single sheet is used, inthe present invention it may be possible to use a polarizer comprised ofa plurality of sheets including a retardation film and optical film forviewing angle compensation.

A polymer network type liquid crystal display element and polymerdispersed type liquid crystal display element may be used as the opticalelement 62. For example, it may be possible to use the polymer networktype liquid crystal display element with an arrangement as shown in FIG.8.

FIG. 8 is a sectional view showing an arrangement of the optical elementof the transflective liquid crystal display device according toEmbodiment 2 of the present invention. The transparent electrode 33 isformed on one main surface of one side of the glass substrate 31. Thetransparent electrode 34 is formed on one main surface of the other sideof the glass substrate 34. The same materials as those used in theliquid crystal panel 63 may be used as materials for the transparentelectrodes 33 and 34, and as methods of forming the electrodes, theremay be methods used in manufacturing general liquid crystal displaydevices. In addition, in the arrangement, since the transparentelectrodes 33 and 34 respectively on the glass substrates 31 and 32 donot need to compose matrixes of scanning electrode and signal electrode,the need of patterning is eliminated in a display region with regard tothe transparent electrodes formed on the optical element 62, andfurther, positioning is not required in assembling the liquid crystalpanel 63, thus enabling simplified processes.

The polymer liquid crystal layer 35 is formed between the glasssubstrates 31 and 32. The polymer liquid crystal layer 35 is sandwichedbetween the glass substrates 31 and 32 arranged so that the transparentelectrodes 33 and 34 are opposed to each other. As the polymer liquidcrystal layer 35, it may be possible to use a polymer network typeliquid crystal where networks containing liquid crystal molecules extendin a polymer matrix and a polymer dispersed type liquid crystal whereliquid capsules containing liquid crystal molecules are dispersed in apolymer matrix. In addition, in terms of low driving voltage, thepolymer network liquid crystal is more advantageous.

The liquid crystal panel 63 and optical element 62 are arranged in theorder of the backlight 61, optical element 62 and liquid crystal panel63 as shown in FIG. 6. This arrangement uses light from the backlight 61in the transmissive mode, while using the external light in thetransflective mode. Therefore, the switching control is performed suchthat the optical element 62 is the transmissive state in thetransmissive mode, while being the scattering state in the reflectivemode.

FIG. 9 is a block diagram showing an arrangement of the transflectiveliquid crystal display device according to Embodiment 2 of the presentinvention. The arrangement has the control section 41 that controls theentire device, switching control section 42 that controls switching ofapplication of voltage to the backlight 61 and optical element 62, andpower supply 43 that supplies the power for the application of voltage.Further, the arrangement has switches SW5 and SW6 to perform switchingcontrol.

The operation in the transflective liquid crystal display device withthe above-mentioned arrangement according to this embodiment will bedescribed below.

Based on an input from a user or external circumstances (such asluminance and quantity of light), the control section 41 automaticallysets a display mode (reflective mode or transmissive mode), and outputsthe mode information to switching control section 42. The switchingcontrol section 42 controls switching of power supply to SW5 and SW6 soas to use the light from the backlight 61 in the transmissive mode,while using the external light in the reflective mode.

A case of the reflective mode will be described first. In the reflectivemode, since the optical element 62 is used as a reflector, SW5 is OFF(scattering state). In the reflective mode, since the external light isused, the power is not supplied to the backlight 61. Thus, SW6 is OFFeither.

In such a state, the external light is passed through the liquid crystalpanel 63, reflected by the optical element 62 of the scattering state,passed through the liquid crystal panel 63 again and then output to theoutside (arrow B in FIG. 6). The liquid crystal panel 63 operates as aliquid crystal display element. In other words, the power supply 43supplies the power to apply the voltage to the liquid crystal panel 63for the display.

A case of the transmissive mode will be described next. In thetransmissive mode, since the optical element 62 passes the light fromthe backlight 61, SW5 is ON (transmissive state). In the transmissivemode, since the light from the backlight 61 is used, the power issupplied to the backlight 61. Therefore, SW6 is ON also.

In such a state, the light from the backlight 61 is output to theoutside through the optical element 62 of the transmissive state andliquid crystal panel 63 (arrow A in FIG. 6). The liquid crystal panel 63operates as a liquid crystal display element. In other words, the powersupply 43 supplies the power to apply the voltage to the liquid crystalpanel 63 for the display.

Thus, in the transflective liquid crystal display device according toEmbodiment 2, since the optical element, which switches betweentransmission of light from the backlight and reflection of externallight by applying the voltage, is arranged between the backlight andliquid crystal panel, well-lighted display can be realized in either thetransmissive mode or the reflective mode using the whole pixels. Inother words, it is possible to deliver optimum performance in both thetransmissive mode and the reflective mode. Further, in this embodiment,it is not required to provide a transmissive region (hole) in a pixel,thereby enabling simplified manufacturing processes.

This embodiment describes the arrangement where the optical element isarranged between the liquid crystal panel and backlight, and further,the present invention allows an arrangement where an optical element isincorporated into a liquid crystal panel such that the optical elementis arranged between a liquid crystal layer and backlight.

While this embodiment describes the arrangement where application ofvoltage to the optical element 62 is switched, by using an arrangementwhere the scattering degree is associated with grayscale in a polymerliquid crystal of the optical element 62, it is possible to realizegrayscale display by performing both the reflective display andtransmissive display. In this case, the power is applied to all theoptical element, liquid crystal panel and backlight, and the voltageapplied to the optical element is controlled. It is thereby possible tocontrol priorities of modes to use in user preferential.

The present invention is not limited to above-mentioned Embodiments 1and 2, and is capable of being carried into practice with variousmodifications thereof. For example, while Embodiments 1 and 2 describethe case of using a passive type liquid crystal display element as aliquid crystal panel and optical element used as a display element, thepresent invention allows the use of an active matrix type liquid crystaldisplay element.

Further, while Embodiments 1 and 2 describe the case of using a polymernetwork type liquid crystal display element as an optical element, thepresent invention is capable of being applied to a case of using apolymer dispersed type liquid crystal display element. Furthermore, anoptical element that electrically controls switching between its stateswhere light is passed through and where light is reflected may be usedas an optical element in the present invention, as well as opticalelements using a polymer network type liquid crystal display element orpolymer dispersed type liquid crystal display element.

Moreover, while Embodiments 1 and 2 respectively describe the case ofusing the optical element 13 or 62 with the polymer liquid crystal layer35 sandwiched between glass substrates, the present invention is capableof being applied to a case where the optical element 13 or 62 is a filmwithout using glass substrates. This case enables the optical element tobe bonded to the liquid crystal panel, and thus allows simplifiedmanufacturing processes.

The present invention enables adequately well-lighted display in bothmodes, transmissive mode and reflective mode, and therefore, is capableof being applied to liquid crystal display devices such as cellulartelephones and PDA (Portable Digital Assistant) used in externalenvironments.

As described above, since the transflective liquid crystal displaydevice of the present invention has an optical element, which switchesbetween transmission of light from the light source and reflection ofexternal light by applying the voltage, is arranged between a lightsource and liquid crystal panel or over a liquid crystal panel,well-lighted display can be realized in either the transmissive mode orreflective mode using the whole pixels.

This application is based on the Japanese Patent Application No2002-220846 filed on Jul. 30, 2002, entire content of which is expresslyincorporated by reference herein.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A transflective liquid crystal display device with a reflective modeusing external light and a transmissive mode using a light source,comprising: a light source for use in the transmissive mode; a liquidcrystal panel, arranged over said light source, operating as a firstdisplay element in the transmissive mode and being turned off in thereflective mode; and an optical element comprising an arrangement ofpixels and a color filter, over said liquid crystal panel, for operatingas a second display element in the reflective mode without using atransflector and for operating as a color filtering unit in thetransmissive mode.
 2. The transflective liquid crystal display deviceaccording to claim 1, wherein said optical element passes light fromsaid light source in the transmissive mode and reflects said externallight in the reflective mode.
 3. The transflective liquid crystaldisplay device according to claim 1, further comprising switchingcontrol means for switching control of the power supply such that saidliquid crystal panel and said light source are turned on in thetransmissive mode and turned off in the reflective mode.
 4. Thetransflective liquid crystal display device according to claim 1,wherein said optical element is full-transmissive in the transmissivemode.
 5. The transflective liquid crystal display device according toclaim 1, wherein said optical element has a polymer dispersed typeliquid crystal display element or a polymer network type liquid crystaldisplay element.